Aedes triseriatus is a tree hole-breeding mosquito that is a vector of LaCrosse encephalitis virus. Across its range, A. triseriatus encounters vastly different biotic and antibiotic environments. Predation on larvae by Toxorhynchites rutilus, the length of the active season, and number of potential competitors all increase from north to south. Correlated with these environmental differences are differences in vulnerability to predation, vulnerability to starvation, population growth rate, and behavior. Analysis of geographic variation in A. triseriatus is important for understanding the medical impact of this species. The long term goal of this research is to test hypotheses that differing predation, climatic, and/or competitive regimes have selected for geographic differences in population characteristics. During this proposed project, laboratory experiments with several strains of A. triseriatus will test for geographic variation in the relationship of size and fecundity. Behavior of larvae will be compared across several populations to test whether known differences in behavior are consistently correlated with the presence of T. rutilus. Experimental observations will be used to test whether behavioral differences are related to vulnerability to predation. The effects of temperature on geographic differences in population response to predation and food availability will be tested in two experiments. Competitive ability against Aedes albopictus will be determined for several strains of A. triseriatus, in order to test the hypothesis that competitive ability is consistently correlated with the presence of T. rutilus.